Data storage apparatus and method for handling a data storage apparatus

ABSTRACT

Real-time audio video applications require guaranteed request service times from a hard disc drive. This requirement is not always fulfilled due to some unexpected delays in service times. One of the causes of such delay is the replacement of defective or bad sectors. By putting spare sectors on each track and extending the track skew in combination with read-and-write-on-arrival strategies it is possible to prevent extra delays in service times due to replacement of sectors.

The invention regards a data storage apparatus comprising a data storagemedium formatted in a pre-determined architecture comprising a pluralityof at least one format feature, and having a user area and a spare areadefined thereon. Further the invention regards a method for handling adata storage apparatus comprising a data storage medium formatted in apre-determined architecture having a plurality of format features, andhaving a user area and a spare area defined thereon, wherein upon a datarequest of a host a controller provides at least one format feature ofthe data and wherein the medium is rotated and a head is moved andactuated to access the format feature to transfer data therewith.

Hard disc based devices recording e. g. multimedia streams likeMPEG-encoded video require real-time file system for writing the data toa disc and for reading the data back. Real-time file systems try towrite all files in time but sometimes cannot succeed for example becauseof disc problems. Conventionally there are then two options: writing thedata too late, or discarding some of the unwritten data. The firstoption will typically cause buffer overflows for recording, which maylead to a significant data loss. The second option may also result in adata loss. Traditional data oriented operating systems have no real-timerequirements and attend to aim for a maximum data integrity, delayingcompletion of each command until properly executed.

In particular real-time audio video applications require guaranteedrequest service times from a hard disc drive. This requirement is notalways fulfilled due to some unexpected delays in service time. Replacedsectors i. e. data of defect sectors allocated to remote spare areas ona disc are one of the reasons for such delays. The delays mainly resultfrom searching replaced sectors and from accessing the remote spare areathe defect sector data have been allocated to. Such remote spare areaconventionally is located in a track or tracks other than the originallyaccessed track of the defect sector. Therefore, track switching as wellas seek time causes such delay.

In the U.S. Pat. No. 6,101,619 a scheme is provided to reduce the numberof searches by accessing replaced sectors at preferably later timessubsequent to a usual data access. In the U.S. Pat. No. 5,166,936 or theWO 98/03970 low level formatting of tracks is suggested to build goodtracks of data to prevent a further access of a defect. Such measurestake considerable effort and may only be done in idle time. Moreoversuch transaction system should be guarded against power failures. Spareareas are conventionally provided as remote spare areas in form of sparearea tracks as for example disclosed in the U.S. Pat. No. 6,201,655 andthe U.S. Pat. No. 5,822,142.

These schemes still require for a track switch and therefore, still arenot able to guarantee a request service time in case of an access to adefective region or a block that contains defect, replaced or allocatedsectors.

To compensate for the time needed by a read/write-head to switch trackfor accessing sequential data, corresponding sectors of each twoadjacent tracks may be skewed i. e. corresponding sectors of each twoadjacent tracks are mutually shifted in the circumferental direction.This allows a read/write-head of a disc drive to essentially arrivedirectly at a first sector of an adjacent track after a track switch.Such first sector may also be referred to as a start sector in thefollowing.

According to the U.S. Pat. No. 5,568,606 a skew is provided to amultiple disc stack in order to synchronise the phase of rotation of thediscs in the multiple disc system upon accessed defects occurring in thesynchronisation zone on the disc. Such method may prevent performancelosses of a multiple disc system due to the need of extra rotations ofone disc upon the occurrence of an accessed effect.

However still such a scheme is not able to guarantee a request servicetime as outlined above.

This is where the invention comes in, the object of which is to specifya data storage apparatus comprising a data storage medium, in particulara disc drive comprising a data storage disc adapted such that a requestservice time can be guaranteed even in case of an access to a region ofthe storage medium that contains defective or replaced sectors. Afurther object of the invention is to specify a method for handling adata storage apparatus comprising a data storage medium by which arequest service time may be guaranteed even in case of an access to aregion of the storage medium containing defective or replaced sectors.

The object regarding the apparatus is solved by a data storage apparatuscomprising a data storage medium, in particular a disc drive comprisinga data storage disc, formatted in a pre-determined format architecturecomprising a plurality of at least one format feature having a user areaand a spare area defined thereon, wherein according to the invention theformat architecture provides a plurality of spare area arrays, whereineach of the spare area arrays is respectively assigned to essentiallyeach of the plurality of the at least one format feature.

Advantageously the apparatus may further comprise a read/write-head, adrive to rotate the disc and a servo to move the head.

It was realised, that even if data originally scheduled to a defectregion are allocated or replaced or re-mapped to a remote spare regionon a track or several tracks other than the originally accessed track ofthe defect, this may cause significant performance losses. Therefore, itis the main idea to provide essentially in each of a format feature of adisc, in particular in essentially each track at least one spare areaarray. This has the advantage that, if a defect should be accessed, datarelated to a defect may be transferred to the spare area array in thesame format feature, in particular in the same track. Therefore, aswitch of the format feature, in particular a switch of a track, isunnecessary to allocate the data related to the defect into a remotespare area.

Continued developed configurations are further outlined in the dependentapparatus claims.

Any number of spare sectors may be provided and can be selecteddependent on the data storage medium and its format architecture. Thenumber may be selected according to the particular use of a disc drive.At least one spare sector should be provided per track. Five sparesectors per track seems to be a reasonable number. The number may alsorange up to one hundred. The number should be selected considering thetotal number of sectors per format feature and/or data storage mediumand/or storage capacity of one sector.

The number of spare sectors may depend on the format feature, they areassigned to. In general the number of spare sectors is chosen so that onthe one hand upon detection of a defect the data space of the sparesectors is large enough to receive all data related to a defect. On theother hand the data space of the spare sectors may not be selected toolarge as this only would enlarge the spare area, however reduce the freeuser area available for user applications.

In a preferred continued developed configuration the format featureprovides a skew for two adjacent tracks. In particular a skew for eachtwo adjacent tracks is preferred. Such skew is a mutual shift in placeof corresponding sectors of two adjacent tracks in circumferentialdirection. Advantageously sectors of an outer track are shiftedcircumferentially in the direction of rotation of the disc relative tocorresponding sectors of an inner track. In particular it is preferredthat the shift comprises at least the minimum number of sectors passedduring a track switch upon rotation of the disc and/or a number of sparesectors comprised by a spare area array assigned to a respective track.Such development allows a spare area to be passed beyond aread/write-head at least once before a track switch, in particular onceper rotation of the medium. Upon a suitable setting of this skew it maybe achieved that the spare area array is passed beyond the head at leastonce after a track switch, in particular essentially first after a trackswitch. The advantage of this is, that not only start sectors may beavailable for a read/write-process right at the beginning of the trackby the read/write-head, but also a number of spare sectors is available.In particular a conventional skew is set according to the effective timea read/write head needs to switch from one track to an adjacent trackand settle on the adjacent track. The skew of the continued developmentof the apparatus is extended and set to account for the size of thespare area and the effective time a read/write-head needs to switch fromone track to an adjacent track and settle on the adjacent track.

The skew may be extended by a number of sectors of one to ten. Inparticular the format architecture advantageously provides a parameterfor the skew in correlation with the size of the spare area array. Thetotal skew should be large enough to account for settle time of the headand the number of spare sectors. Also the skew should be as small aspossible to avoid significant performance loss.

In a further preferred continued developed configuration the datastorage apparatus proposed comprises a controller having a controlelectronics, a microprocessor and a memory. In particular the memorycomprises a buffer memory adapted for intermediate storing of data.Moreover the controller is adapted to record the intermediate storing.Further an interface for connecting the storage apparatus to a host isprovided. This development allows a read/write-head to transfer dataimmediately on arrival on a format feature, in particular on a track ofa data storage disc. Such data may be stored in a buffer memory, thestoring being recorded by the controller and subsequent upon completionof the data transfer the data storage in the buffer memory may betransferred to a host by an interface in correct logical order. Alogical order of data may not be accounted for by immediate datatransfer on arrival. However the read-out of the buffer memory can beperformed that way according to the records of the controller.Advantageously the development saves rotational latency time as a datatransfer may take place independent of the logical order of the data.

Further the invention leads to a method for handling a data storageapparatus, in particular to a data storage apparatus as described. Suchdata storage apparatus comprises a data storage medium formatted inpredetermined architecture having a plurality of format features andhaving a user area and a spare area defined thereon, wherein upon a datarequest of a host a controller provides at least one format feature ofthe data, in particular at least a track and a sector, and wherein themedium is rotated and the head is moved and actuated to access theformat feature to transfer data therewith. The above object regardingthe method is solved by such method, wherein according to the inventioneach of the spare area arrays is respectively assigned to essentiallyeach of the format features such that a spare area is passed beyond thehead at least once before a track switch.

Continued developed configurations are further outlined in the dependentmethod claims.

In particular the format feature is selected from the group consistingof: zones, cylinders, tracks and blocks, in particular a track.Advantageously a spare area is passed beyond the head at least onceafter a track switch, in particular essentially first after a trackswitch. Preferably the spare area array is passed beyond the head atleast once per rotation of the medium.

In a preferred configuration the data are transferred as soon as thehead is positioned on the format feature, in particular the track,determined by the controller. In still a further preferred configurationof the invention the data are sequentially transferred and areintermediately stored in sequential order in a buffer memory and thedata transfer is recorded by a controller and subsequent the data areread-out from the buffer memory and are transmitted to the host inlogical order.

The invention will now be described with reference to the accompanyingdrawing. The figures of the drawing illustrate in a schematic and notnecessarily scaled form preferred embodiments of the invention comparedto prior art. The figures illustrate in:

FIG. 1: a hard disc drive of prior art;

FIG. 2 a: a hard disc drive of prior art with remote spare areas;

FIG. 2 b: a hard disc drive of prior art with conventional skew;

FIG. 2 c: a hard disc drive of prior art with conventional skew andindicated motion a read/write-head during a track switch;

FIG. 3 a: a scheme of sector skipping and slipping in the preferredembodiment;

FIG. 3 b: an allocation and mapping scheme for a defective sector due toa grown defect into a spare area in the preferred embodiment;

FIG. 4 a: a non-remote allocation of spare sectors being part of sparearea arrays on a hard disc drive in a preferred embodiment;

FIG. 4 b: an extended skew on a hard disc drive taking into accountspare area arrays on each track according to a preferred embodiment;

FIG. 4 c: an extended skew on a hard disc drive taking into accountspare area arrays on each track and indicated motion of aread/write-head during track switch according to a preferred embodiment;

FIG. 5: an example for a scheme providing data transfer on arrival usinga buffer memory according to a further preferred embodiment.

FIG. 1 illustrates the structure of a hard disc drive 1 comprising adata storage disc 2, a read/write-head 3, a drive, which is not shown,to rotate the data storage disc 2 around a spindle 4 and a servo, whichis not shown, to turn the head 3 around an axis 5 to move the head 3 toa pre-determined position on the disc 2 to transfer data therewith. Thehead 3 is controlled by a read-and-write electronics and a servoelectronics being part of the controller 6 of the disc drive. Thecontroller 6 further comprises a formatter electronics which upon a datarequest converts such request into corresponding numbers of formatfeatures of the disc 2. Such data request may be received from a host 7by an interface and an interface electronics. Further the controller 6comprises a microprocessor, ROM and RAM e. g. a buffer memory.

The disc 2 contains according to a format architecture a plurality offormat features of the kind selected from the group of zones 9, 10, 11each comprising a plurality of tracks 8. A track is divided into aplurality of blocks 12, 13, 14. Preferably all blocks 12, 13 and 14 havethe same size of data capacity. As the number of blocks per track mayvary from to track to track or zone to zone some of the blocks may bedivided by servo wedges 15. Servo wedges may also be evenly spacedradially around the disc like spokes on a wheel. If the disc drive 1should contain multiple heads 3 for multiple discs 2 then the tracks 8of a disc 2 and the corresponding tracks 8 of the further discs being atthe same radius are referred to as a cylinder. In this case each trackassigns a respective cylinder. Further in a conventional drive a remotespare area 16 is provided on the disc 2 as a track or plurality oftracks at the inner circumference of the disc 2.

The number, size and allocation of remote spare areas 16 may bedifferent for different hard disc drives depending on the manufacturerand product family. For instance there can be a number of remote spareareas 16 evenly spaced in the address space as indicated in FIG. 2 a.Also there may be just one remote spare area 16 located at the innerdiameter, outside the user addressable area as shown in FIG. 1.

Each data storage apparatus and in particular disc drive may havedependent on its structure and handling a maximum service time. Themaximum service time of a drive is the total time of the data transferand the maximum access time and can be calculated using the formulaT=AX+B. The parameter A is the transfer time of a single sectorexpressed in time per sector. The parameter X is the number of sectorsto be transferred and the parameter B is the maximum access time whichis the sum of seek time and rotational latency time. Rotational latencytime may in particular but not only result when the read/write-head hasto switch to a next track. In the preferred embodiment of the inventionthe latter may be advantageously restricted to one full rotation.

There are cases where a conventional drive is not able to finish arequest within this maximum service time. Examples of such cases areretries due to an error correction code error, servo errors due toshocks and vibrations and hard errors. Hard errors are caused by mediadefects and are handled conventionally by the defect management of adrive. When an error correction code error cannot be corrected withseveral retries it is possibly caused by a media defect. To verify thatthe error was caused by a media defect, the drive performs a media teston each defective sector. The media test consists of write/readverifies, wherein the suspicious sectors are written and read severaltimes. If any of them fails then the sector is a grown defect and isconventionally allocated to a remote spare sector. Defects that occur inthe field are referred to as grown defects in the following.

FIG. 2 a shows a schematic view of a data storage disc with a head 3 anda plurality of tracks 8 containing two remote spare areas 16.

FIG. 2 b illustrates schematically a conventional track skew of an outertrack 8 a adjacent to an inner track 8 b upon an angle 18 incircumferental direction in the direction of rotation 19 of the disc 2.Corresponding start sectors of the tracks 8 a and 8 b are depicted as 20a and 20 b. As shown in FIG. 2 b a track skew may be employed in harddisc drives to minimise rotational latency time that results when thedrive has to switch to a next track to access sequential data. This isdepicted by the motion 21 of the head 3 in FIG. 2 c. Conventionally askew is large enough to make sure the head 3 has enough time on the nexttrack 8 b to settle.

Track skewing provides a mutual shift of corresponding sectors inadjacent tracks in a circumferental direction relative to each other.Due to track skewing e. g. corresponding sectors of tracks are notlocalized in radial direction along a straight line but instead alongbended lines 17 such as depicted in FIG. 1.

Further in FIG. 2 c reference mark 22 depicts a read/write-operation and23 a seek operation. To prevent seek operations during sequential datatransfers it is advantageous to prevent defective sectors to bereallocated to remote spare areas.

Conventionally only during manufacturing defective sectors are skipped.

In a preferred embodiment as shown in FIG. 3 a a defective sector 3occurred during use of the data storage apparatus, known as a growndefect, may be replaced by a next immediate spare sector in order tomaintain the sequential ordering of logical data sequences. Thistechnique eliminates the need to seek to another track to access areplacement of an sector allocated in a remote spare area. If defects,known as grown defects, occur during application of a hard disc drive,such skip and slip scheme is applied during an application, i.e. in thefield, in the preferred embodiment. It is applicable within a wide andunlimited range, as a spare area may be provided for essentially each ofa plurality of at least one format feature, in particular a track.Conventionally defects that occur during application are, if found,allocated to a remote spare sector at another track.

In the situation depicted in FIG. 3 b, the physical sector PBA 3 isallocated to the replacement sector S2 in a spare area array on the sametrack. Therefore such spare area array is not a remote spare area. Thelogical address LBA 3 is mapped to the replacement sector S2 in thespare area array on the same track. Converting the physical sector PBA 3into a slipped sector in the field, is indicated in FIG. 3 a. Thisallows in the field for not only a shift in the logical to physicaladdress mapping but also for a shift of a content of the correspondingsectors. In the example of FIG. 3 b this means that the logical blockaddress LBA 3 will be mapped on the physical block address PBA 4, LBA 4will be mapped on PBA 5, LBA 5 will be mapped on PBA 6 and so on.

In a further development at the same time the content of PBA 3 which islocated at the replacement sector S2 on the same track can be moved fromS2 to PBA 4 and the content of PBA 4 has to be moved to PBA 5 and so on.This slipping in the field should continue until a free sector e. g. aspare sector of the spare area of the same track is reached. Otherwise,a discontinuity in the logical to physical mapping exists as it is thecase e. g. when a sector is allocated to a remote replacement sector onanother track.

Conventionally the allocation process of a defective sector causes anextra delay in service time of a disc drive. When the drive 1 encountersa defective sector and decides to allocate it to a remote spare area 16,the head 3 is moved from the track 8 with the defective sector in theuser area to a track 8 where spare sectors are allocated in a remotespare area 16. When the right spare sector is rotated under theread/write-head 3, the data is written to the spare sector. Subsequent,if the drive has to resume reading or writing, the head is moved back tothe original track 8 where the defective sector was found. This processcosts extra time due to searching and accessing the sector allocated inthe remote spare area 16: the head 3 has to move to the spare sector ina remote spare area 16 to read or write at the spare sector and the head3 has to move back to track 8 to resume reading or writing. In areal-time audio-video application therefore, conventional methods forhandling data and a conventional data storage apparatus may notguarantee a maximum service time in case an error occurs. Alternativelydelivering erroneous or incomplete data to the host 7 and reporting theerror has to be taken into account. When accessing a data pool with oneor more erroneous sectors, the drive will also be unable to finish therequest within the maximum service time.

The embodiment illustrated in FIG. 4 a provides spare sectors 30 on eachtrack 31 to prevent a seek action to a remote spare sector. Doing soguarantees maximum service time even in cases, in which a defect sectoris accessed. When requested data are located on one track and withintrack boundaries, they can be transferred within one disc revolution,even if it contains re-allocated sectors as long as the number ofre-allocated sectors does not exceed the number of spares 30 on thetrack 31. A multiple number of complete tracks can also be transferredwithin the maximum service time, even if each track contains a limitednumber of re-allocated sectors in the spare area 30 of each trackaccording to the preferred embodiment.

In a further preferred embodiment the track skew is improved. Forinstance when a requested pool of data lies across track boundaries andis not a multiple number of complete tracks and is not aligned withphysical tracks and contains replaced sectors on the last track, itcannot be transferred by conventional methods within the maximum servicetime. Specifically if one is to transfer two consecutive sectors lyingon consecutive tracks, e. g. the last sector of track n and the firstsector of track n+1 depicted in FIG. 4 b, under the assumption that thefirst sector of track n+1 is defect and is allocated to a spare sectorlocated at the end of the track, in the worst case one has to wait onefull rotation to access the sector on track n. After the head isswitched to the next track one has to wait another full rotation toaccess the replaced sector. In this case the service time exceeds themaximum service time by almost one full rotation, i. e. to be precise,one full rotation minus the transfer time of one sector.

Such performance can be solved if the spare sectors are accessed firstafter a track switch. As shown in FIG. 4 b and by the motion 41 of theread/write-head 3 in FIG. 4 c the problem can be solved by extending theconventional track skew 18 according to the preferred embodiment to anextended track skew 48. The extension is adapted such that the sparesectors 40 b are always accessed first after a track switch 41 and thespare sectors 40 a are always accessed before a track switch 41. Asillustrated by the motion 41 of the read/write-head 3 spare sectors 40 aare always accessed before a track switch 41 in order to guaranteemaximum service time when the pool of requested data starts in themiddle of a track n. Further the spare sectors 40 b also are accessedafter a track switch 41, preferably first after a track switch 41, toguarantee maximum service time for a requested pool of data which endsat the middle of a track n+1. In general the spare sectors 30, 40 a, 40b in FIGS. 4 a, 4 b and 4 c are at least accessed once per revolution ofa disc 2. Thereby, the maximum service time is guaranteed even whenaccess to a replaced sector has to be made. This scheme is successful aslong as the number of defective sectors does not exceed the number ofspare sectors 30 allocated on each track 31. Therefore, the number ofspare sectors may be suitable set on demand.

A further continued developed embodiment prevents extra delays in theservice time by applying a read-and-write-on-arrival strategy asindicated in FIG. 5. Such strategy is also referred to astransfer-on-arrival strategy or zero-latency-read or out-of-order-readstrategy. This developed embodiment allows a drive 1 according to apreferred embodiment to start reading and writing data as soon aspossible after the read/write-head 3 is positioned on the rightrequested track. If on arrival the last part of the requested data ispassing under the head 3, then this part of the data is read into adrive's buffer first e. g. RAM or ROM. This is referred to in FIG. 5 by52 with regard to the sectors S₁ to S_(m) following the seek position50. Upon further rotation 51 of the disc 2 under the head 3 theremaining part of the data in sectors S₀ to S₁₋₁ following the startsector of the respective track are read into the drive buffer as thedisc 2 rotates under the head 3. This is referred to by 53 in FIG.5.When requested data are stored in the drive's buffer, the requesteddata are transferred from the drive's buffer to the host, preferably insequential order.

Similar to the described read-on-arrival strategy is thewrite-on-arrival strategy. The data do not have to be written to thedisc 2 in the right order. Once the data is in the drive's buffer e. g.RAM or ROM the last part of the data may by written to the disc 2 firstand then the remaining part of the data.

Read-and-write-on-arrival strategies, i. e. transfer-on-arrivalstrategies, reduce the rotational latency time for disc accesses. Inconventional methods for handling data a seek is required for theaccess. The conventional read strategy provides that the drive waits fora start sector of a requested data pool to pass under the head 3 oncethe head 3 is positioned on the right track. This causes substantialperformance losses.

Therefore, the advantage of the read-and-write-on-arrival strategy as adevelopment of the preferred embodiment, is that the maximum servicetime is shorter than the conventional maximum service time.

In particular this is a achieved when the transfer length S_(o) to S_(m)is shorter than a track and no track boundaries are crossed. In such acase the maximum service time with transfer-on-arrival strategy isspecifically a seek time plus one disc revolution. This is assigned bythe parameter B being the maximum access time which is the sum of seektime and rotational latency time. Data transfer may be provided parallelto the data access.

In comparison in a conventional strategy the maximum service time willalways be described by the formula AX+B, i. e. the transfer time plusseek time plus at most one disc revolution.

When a request block lies across track boundaries or is not a multiplenumber of complete tracks or is not aligned with physical tracks andcontains replaced sectors on the last track, such a problem is solved byapplying extending the track skew 48 such that these spare sectors 40 a,40 b are always accessed first after a track switch and always accessedbefore a track switch. This way the maximum service time is guaranteedwhen accessing re-allocated sectors as long as the number of defectivesectors does not exceed the number of spare sectors 30, 40 a, 40 ballocated on each track 31.

Further the combination of the outlined strategy of spare sectors 30, 40a, 40 b on each track and extended track skew 48 may be combined withread-and-write-on-arrivals strategies of FIG. 5 to establish a veryefficient tool to guarantee maximum service times.

In particular the number of spare sectors 30, 40 a, 40 b to be allocatedon each track, as spare sectors in a spare area array per track 31depends on the number of sectors per track, the grown defect statisticsof a drive and how much drive capacity can be sacrificed. Current harddisc drives have about five hundred sectors per track on average.Putting five spare sectors on each track means 1% decrease in capacity.Such slight decrease is acceptable and may even be extended to 2% or 3%.Moreover, a decrease in number of sectors per track due to spare sectorsand extended skew time results in a slight decrease in data throughputof a drive. However such decrease in sustained data rate of a drive isclearly less than 2%, so that the minimum data transfer time may beslightly raised.

For example a hard disc drive may be rotated with 5400 rotations perminute, providing 500 sectors per track and 3 ms track skewcorresponding to a rotation time of 11.2 ms and a sustained datatransfer rate of 17.19 MB/s. The sustained data transfer rate isdetermined according to the formula:${{data}\quad{transfer}\quad{rate}} = \frac{{sector}\quad{per}\quad{track}}{{{rotation}\quad{time}} + {skew}}$

Preferably five spare sectors on each track may be suitable, so that thetrack skew should be extended by 112 μs, which corresponds to therotation time of five sectors. So the extended track skew 48 has become3.112 ms and the number of sectors per track 495. The correspondingsustained data rate is 16.89 MB/s which corresponds to a 1.77% decreasein the sustained data transfer rate of the drive.

Such reduced data transfer rates and address capacity is only anegligible sacrifice in view of the fact that the allocation strategy asproposed guarantees maximum request service time even when replacedsectors must be accessed by the drive to execute the request. It openspossibilities to separate media-test for suspicious sectors from thereplacement process, or to turn replaced sectors into slipped sectorsfor example when a sector must be replaced to a spare sector on anothertrack, because the spares on the same track are used up.

While there has been shown and described what is considered to bepreferred embodiments of the invention, it will of course be understoodthat various modifications and changes in form or detail could readilybe made without departing from the spirit of the invention. It istherefore intended that the invention may not be limited to the exactform and detail herein shown and described nor to anything less than thewhole of the invention herein disclosed and as herein after claimed.

The invention may be summarised as follows:

Real-time audio video applications require guaranteed request servicetimes from a hard disc drive. This requirement is not always fulfilleddue to some unexpected delays in service times. One of the causes ofsuch delay is the replacement of defective or bad sectors. By puttingspare sectors on each track and extending the track skew in combinationwith read-and-write-on-arrival strategies it is possible to preventextra delays in service times due to replacement of sectors.

1. Data storage apparatus (1) comprising a data storage medium (2), inparticular a disc drive (1) comprising a data storage disc (2),formatted in a pre-determined format architecture comprising a pluralityof at least one format feature (8, 9, 10, 11, 12, 13, 14), and having auser area and a spare area defined thereon, characterised in that theformat architecture provides a plurality of spare area arrays (30, 40 a,40 b) wherein each of the spare area arrays (30, 40 a, 40 b) isrespectively assigned to essentially each of the plurality of the atleast one format feature (8, 9, 10, 11, 12, 13, 14).
 2. Data storageapparatus as claimed in claim 1, characterised in that essentially eachof a plurality of tracks (8) comprises at least one spare area array(30, 40 a, 40 b).
 3. Data storage apparatus as claimed in claim 1,wherein a spare area array (30, 40 a, 40 b) comprises at least one andup to one hundred spare sectors, in particular up to ten, advantageouslyfive spare sectors per track.
 4. Data storage apparatus as claimed inclaim 1, characterised in that the format architecture provides a skew(18, 48) for two adjacent tracks (n, n+1) being a mutual shift in placeof corresponding sectors of two adjacent tracks (n, n+1) incircumferental direction (19).
 5. Data storage apparatus as claimed inclaim 4, characterised in that sectors of an outer track (n) are shiftedcircumferencally in the direction of rotation of the disc relative tocorresponding sectors of an inner track (n+1), wherein in particular theshift comprises at least the minimum number of sectors passed during atrack switch upon rotation (19) of the disc and/or a number of sparesectors (40 a, 40 b) comprised by a spare area array assigned to arespective track.
 6. Data storage apparatus as claimed in claim 4,characterised in that a skew is extended by a number of sectors of oneto ten.
 7. Data storage apparatus as claimed in claim 4, characterisedin that the format architecture provides a parameter to set the skew(48) in correlation with the size of the spare area array (30, 40 a, 40b).
 8. Data storage apparatus (1) as claimed in claim 1, characterisedin that a controller (6) having a control electronics, a microprocessorand a memory is provided wherein a buffer memory (RAM, ROM) is adaptedfor intermediate storing of data and the controller (6) is adapted torecord the intermediate storing, wherein further an interface forconnecting the storage apparatus to a host (7) is provided.
 9. Methodfor handling a data storage apparatus (1), in particular a data storageapparatus (1) according to claim 1, comprising a data storage medium (2)formatted in a pre-determined architecture having a plurality of formatfeatures, and having a user area and a spare area defined thereon,wherein upon a data request of a host a controller (6) provides at leastone format feature of the data, in particular at least a track and asector, and wherein the medium (2) is rotated (19) and a head (3) ismoved and actuated to access the format feature to transfer datatherewith, characterised in that the format architecture provides aplurality of spare area arrays (30, 40 a, 40 b), wherein each of thespare area arrays (30, 40 a, 40 b) is respectively assigned toessentially each of the format features such that a spare area (30, 40a, 40 b) is passed beyond the head (3) at least once before a trackswitch (41).
 10. Method as claimed in claim 9, characterised in that theformat feature is selected from the group consisting of: zones (9, 10,11), cylinders (8), tracks (8) and blocks (12, 13, 14).
 11. Method asclaimed in claim 9, characterised in that a spare area array (30, 40 a,40 b) is passed beyond the head (3) at least once after a track switch(41), in particular essentially first after a track switch (41). 12.Method as claimed in claim 9, characterised in that the spare area array(30, 40 a, 40 b) is passed beyond the head (3) at least once perrotation (19) of the medium (2).
 13. Method as claimed in claim 9,characterised in that data are transferred as soon as the head (3) ispositioned on the format feature, in particular track (8), determined bythe controller (6).
 14. Method as claimed in claim 13, characterised inthat the data are sequentially transferred and are intermediately storedin sequential order in a buffer memory (RAM, ROM) and the data transferis recorded by a controller (6) and subsequent the data are read outfrom the buffer memory (RAM, ROM) and are transmitted to the host (7) inlogical order.